The general objective of this research is to determine the three- dimensional geometries of biologically active molecules and to correlate these geometries with their biological activity and their evolution. In particular, the high-resolution structures of several groups of proteins are being examined by X-ray crystallographic methods: they include Serine proteases and their precursors, cytochromes, the non-heme iron proteins and dihydrofolate reductases. Bibliographic references: "Crystallographic Structure Refinement of Chromatium High Potential Iron Protein at 2 Angristrom units Resolution," S.T.Freer, R.A. Alden, C.W. Carter, and J. Kraut, J. Biol. Chem. Approximatey 250, 46 (1975); "X-ray Crystallographic Study of Boronic Acid Adducts with Subtilisin BPN' (Novo): A Model for the Catalytic Transition State," D.A. Matthews, R.A. Alden, J.J. Birktoft, S.T. Freer, and J. Kraut, J. Biol. Chem. approximately 250, 7120 (1975).